// https://leetcode.cn/problems/divisible-and-non-divisible-sums-difference/description/

func differenceOfSums(n int, m int) int {
    a, b := 0, 0
	for i := 1; i < n + 1; i++ {
		if i % m == 0 {
			a += i
		}
		b += i
	}
	c := b - a
	return c - a
}